Size in the world of lighting refers to the wattage size of the fluorescent bulbs being used. Before buying fluorescent ballasts, you should know what type of fluorescent ballasts are available and why one might be a better than the other.
The word "ballast" identifies a substance or device that provides stability or control. A fluorescent ballast is a device designed to limit or stabilize the amount of electrical current in the circuit that feeds a fluorescent light fixture. The ballast sits between the fixture and the light switch and converts the voltage coming from the electrical service in the home to the correct voltage for the fluorescent fixture.
Ballasts help regulate and reduce energy consumption and assist the fixture to run optimally.
Fluorescent ballasts come in two types: one is electronic and the other magnetic, sometimes called an electromagnetic ballast. The electromagnetic ballast uses a core and coil system to control the electrical current. Electronic ballasts are a more recent addition to fluorescent ballasts and offer some energy savings over electromagnetic ballasts because they use more efficient electronic components to control voltage levels.
The size of a fluorescent ballast must match the requirements of the fluorescent lamp it is connected to. This means the size of the ballast must match the wattage of the fluorescent bulb. For instance, an eight-watt fluorescent lamp will require an eight-watt ballast. Most ballasts are referred to by the wattage they handle, such as a "T8" ballast, which handles an eight-watt lamp. Verifying the specifications of a fluorescent ballast also reveals the number of pins -- the connecting pins of the fluorescent lamp -- it accepts and the voltage it handles. Because electronic ballasts require smaller components, the ballast weighs less and is shorter in length, width and height than electromagnetic ballasts.
Electromagnetic ballasts are less expensive than electronic ballasts. However, the electromagnetic ballast has a humming noise, referred to as ballast noise, that might be irritating in some areas of the home or office. Electromagnetic ballasts are labeled with a noise or sound rating of A to F -- A indicates the quietest type of magnetic ballast. Electronic ballasts do not have a noise issue. Instead, some electronic ballasts interfere with radio and higher frequencies. This indicates the ballasts can be a problem in areas where TVs, radios and sensitive machines, such as medical equipment, are run.